Scientists deliver key info about soy-stabilised soy emulsions

Modifying the ingredients and manufacturing parameters may enhance the stability of soy stabilised emulsions for food, says a new study from Ireland.

Researchers from University of Limerick and Wyeth Nutritionals Ireland report that parameters such a heat pre-treatment, pH and calcium supplementation can all affect the thermal stability of emulsions formulated with commercial soy protein isolates (SPI) and hydrolysates (SPH).

Writing in Food Research International, the researchers note that their’s is the first study to address these parameters on the stability of soy protein-stabilised emulsion systems.

“The information [from this study] should be useful to those involved in the manufacture of soy protein based formulated infant foods and other thermally process emulsified food products,” they wrote.

Recent figures from Frost & Sullivan reveal emulsifiers, along with fat replacers, are leading growth in the food additive industry: since 2001 the market value of emulsifiers rose by some 5.6 per cent. Emulsifiers are used by food makers to reduce the surface tension between two immiscible phases at their interface - such as two liquids, a liquid and a gas, or a liquid and a solid - allowing them to mix.

Study details

The researchers, led by Dick FitzGerald, examined the effects of different thermal pre-treatments (from 70 to 90 degrees Celsius), pH ranges (from 6.4 to 7.5), and calcium addition (450 to 850 mg per litre) on the stability of model emulsion systems stabilised with SPI or SPH.

While no changes in the stability were observed as a result of the thermal pre-treatments, an increase in stability was observed at higher pH levels.

“The higher heat stabilities of the model emulsions at higher pH possibly indicate that intermolecular association between denatured protein molecules may be inhibited due to increased electrostatic repulsion,” wrote the researchers.

“No previous studies appear to address the potential contribution of pre-heating temperature to heat coagulation time of emulsions manufactured with soy protein ingredients,” they added.

Adding calcium decreased stability, on the other hand. Moreover, calcium as calcium chloride led to less stable emulsions than calcium as calcium citrate Comparing SPIs and SPHs, the latter resulted in less stable emulsions, said the researchers.

“[These] results demonstrate that modification of ingredient and manufacturing parameters may be a useful approach for enhancing thermal stability properties of soy protein stabilized emulsions,” they concluded.